The present invention relates to a composition for treating and stabilizing soils, in particular wet soils, comprising, in the form of a powder having a particle size less than 5 mm, quicklime and/or calcium-based hydraulic binders, to the process for preparing such a composition and to the use thereof.
It is known to treat soils, in particular wet soils, in order to dry them and stabilize them, in particular when these soils are intended to serve as foundations for large construction works, such as the construction of roads, car parks, etc. To this end, the soil is mixed with a powdered hydraulic binder or powdered quicklime. These treatments include transferring powdered quicklime or hydraulic binder from the storage reservoir of a spreading vehicle, spreading the powder on the soil to be treated and blending the powder with the soil to be treated, for example by ploughing. In order to achieve suitable transfer conditions, the powder used must be very fluid, i.e. it must have a suitable particle size so that it will flow freely through pipes where transfer is normally made by a pneumatic method. It is moreover appropriate to use a quicklime or binder having a sufficiently fine particle size so as to obtain a dispersion which is as uniform as possible in the soil to be treated and good reactivity. It is usually recommended for example for the foundations of roads, that the quicklime has a particle size which does not exceed 2 mm (see French standard NFP 98-101.
The use of such powders for the treatment of soils has however a certain number of disadvantages, the main one consisting of the emission of lime dust and/or hydraulic binder dust during the treatment described above both during spreading as well as during ploughing. In the presence of wind, it is sometimes possible to observe the transfer of the treatment product by the wind more than 20 to 30 meters from the site area. When this dust is deposited on damp supports or on any unprotected living body, the result is a sudden rise in pH (in the case of lime in particular) or adhesion of the product on these supports following hydraulic setting. The aforementioned dust emissions may thus be aggressive to the environment (corrosion, damage to neighbouring cultivation etc.) and have the effect of leaving visible and tenacious residues on surfaces which it covers, which are unsightly for example in an urban environment (see for example M. SCHAEFFNER and J.-C. VALEUX, Emissions de poussixc3xa8res de chaux et/ou de liants hydrauliques sur les chantiers de traitement de sols et de retraitement de chaussxc3xa9es, rxc3xa9alitxc3xa9et remxc3xa8des; Bulletin de liaison des laboratoires des Ponts et Chaussxc3xa9es, [Dust emissions from lime and/or hydraulic binders on sites where soils are treated and roadways retreated; reality and remedies; Liaison bulletin of the Highways and Bridges Department], 198, July-August 1995).
Processes are known for stabilizing soils in earthworks or for road foundations comprising spreading a lime wash onto the soil to be treated. This type of treatment is only applicable in the case of dry soils, for example in very sunny regions. It is inapplicable in the case of moderately to very wet soils.
A product is also known for stabilizing soil in civil engineering products, including slaked lime, anhydrous or hydrated gypsum and water or an aqueous solution containing an anti-dust agent (see Derwent abstract of JP-5222366 : access number 93-309364). This product uses water or an aqueous solution and, as for the lime wash, it is thus absolutely inappropriate to treat and stabilize soils which are moderately to very wet, as in the case of the present invention.
A surface treatment is also known with quicklime powder, in which the particles of quicklime are coated with an organic compound preferably in solution in an organic solvent. Once these particles are completely coated, the quicklime powder has a distinctly increased resistance to humidity and increased fluidity which improves the conditions of transport and storage (see Japio abstract of JP-58180225). However, when it is necessary to use the powder, it is first necessary to restore its intrinsic reactivity by heating it for ten minutes at approximately 400xc2x0 C. This obviously does not enable it to be considered for the application aimed at by the present invention.
The object of the present invention is to develop a composition for treating and stabilizing soils which meets the requirements of State regulations, while overcoming the disadvantages mentioned above, as well as a process for preparing such a composition and the use thereof.
These problems are resolved by a composition such as indicated at the beginning, additionally including a non-aqueous fluid additive having the power to agglomerate the finer particles of the composition. Advantageously, the composition has a particle size distribution in which the particles smaller than 32 xcexcm represent less than 30% of the total composition, advantageously less than 20% thereof, preferably less than 10% thereof. Also preferably, the composition has a particle size distribution in which the particles larger than 1 mm represent less than 20% of the total composition, advantageously less than 10% and preferably less than 1%.